Text doesn't show up on GtkLabel - gtk

Question

I have this code:
using Gtk;
class ConquerLauncher : Gtk.Application {
protected override void activate() {
var window = new ApplicationWindow(this);
window.add(new InputList());
window.show_all();
}
}
public int main(string[] args) {
return new ConquerLauncher().run(args);
}
class InputList : Box {
public InputList() {
this.set_orientation(Orientation.VERTICAL);
var listStore = new Gtk.ListStore(1,typeof(Label));
var treeView = new TreeView.with_model(listStore);
this.pack_start(treeView);
this.pack_start(new InputBox(this,listStore));
var column = new TreeViewColumn();
column.set_title("Foo bar's");
treeView.append_column(column);
treeView.set_model(listStore);
}
}
class InputBox : Box {
public InputBox(InputList list,Gtk.ListStore store) {
this.set_orientation(Orientation.HORIZONTAL);
var entry = new Entry();
this.pack_start(entry);
var button = new Button.with_label("Add foo bar");
this.pack_start(button);
button.clicked.connect(() => {
var text = entry.text;
entry.text = "";
TreeIter tp;
store.append(out tp);
store.set(tp, 0, new Label(text), -1);
this.show_all();
list.show_all();
});
}
}
What I want to do:
I want to create some sort of input form consisting of three elements:
In an Entry the user should write some text. If the presses the button, it should be added to the TreeView with a ListStore as a model.
Expectation:
The user enters a text, presses the button, the contents of the Entry are added to the TreeView and the text input field is cleared.
Reality:
Everything works, except the label that is added to the TreeView is blank.
Before:
Here an example input:
After pressing the button: